Agyriales

Agyriales is an order of fungi, primarily known for their lichenized growth habit, which often colonize the bark of woody plants. While not always classified as primary parasitic pathogens, their presence on fruit and ornamental trees is frequently associated with reduced tree vigor and bark structural deterioration.

The causative agents are fungi within the class Lecanoromycetes. The type of infection is primarily epiphytic, but excessive colonization by these organisms can significantly impede the bark's physiological processes, including gas exchange through lenticels, which is vital for the tree's overall health.

These fungi mainly affect pome and stone fruit species such as apple, pear, and plum trees, particularly those in neglected or poorly managed orchards. The susceptibility of trees increases as they age or if they suffer from chronic stress, such as poor soil nutrition or waterlogged conditions.

The main symptoms of infestation include the appearance of crusts, scaly patches, or growths on the trunk and main branches. These structures vary in color depending on the species and environmental conditions. If left untreated, the underlying bark may become soft, discolored, and prone to splitting, providing entry points for wood-boring insects.

Environmental conditions that favor the spread of Agyriales include high atmospheric humidity, low light levels, and lack of air circulation within the canopy. The primary harm lies in the creation of a habitat for pests and secondary pathogens, which can severely compromise the plant's structural integrity over several growing seasons.

Effective prevention and control strategies include:

• Regular pruning to improve air circulation and sunlight penetration in the crown.
• Manual removal of bark growths using specialized scrapers or stiff brushes.
• Application of horticultural copper-based sprays during the dormant season.
• Whitewashing trunks to protect the bark from thermal stress and disinfect the surface.
• Improving overall tree health through adequate irrigation and nutrient management programs.